Chemical reaction engineering and its role in the transformation of industries

The development of new processes and the development of apparatus technology for the construction of chemical reactors go hand in hand. Today, the range of apparatus and reactor designs is as broad as the product portfolio of chemical plants. Due to its flexibility, the stirred tank is still the most widely used reactor type. However, the spectrum of technologies ranges from classic fixed-bed reactors with molten salt or evaporative cooling to heat exchange reactors, bubble columns, jet reactors, nozzle and fluidised bed reactors, high-temperature reactors and more complex apparatus such as microstructured, electrochemical and kneader reactors as well as hybrid systems such as reactive distillation, extraction or gas scrubbers.

Although the stirred tank is one of the oldest chemical reactor designs, it is still constantly being improved. New solutions such as flexible baffles and other modifications have been developed for the "inner workings" of enamelled stirred tanks, which have significantly improved the flexibility and energy efficiency of gas-liquid systems despite the otherwise limited production potential of enamelled devices.

In order to increase heat transfer, heat exchanger plates can be introduced into the stirred tank, which offer larger exchange surfaces than internal heat exchange coils. This allows exothermic reactions, such as suspension hydrogenation, to be better controlled. Salt bath reactors are conventional fixed bed reactors for exothermic, heterogeneously catalysed gas phase reactions at high temperatures. They are used, for example, for partial oxidations, such as in the synthesis of acrylic acid.

If the demands on heat exchange or temperature control are higher, so-called heat exchange reactors can be used. Based on plate or tube bundle heat exchangers, they enable very high heat exchange rates for single-phase systems.

The new industrial processes, the change in the energy and raw material base and the pursuit of economic efficiency will continue to pose challenges for reaction technology in the coming years. Particularly in view of the trends towards bio-based and recycled raw materials, whose composition and physical properties vary considerably more than those of conventional petrochemical raw materials and which typically contain far more impurities, reactors must be optimised as far as possible on the one hand, but also robust enough to cope with changing conditions on the other.

For example, some biotechnological processes require large reactor volumes of more than 1,000 m³ and simultaneously high specific mass transfer rates. For a conventional aeration system, motor outputs of more than 10 MW are then quickly required, which is difficult to realise mechanically. The development of hybrid gassing technologies and new ways of dissipating heat could help to bring such processes into industrial application more quickly.

In the production of new gene and cell therapeutics, on the other hand, which are highly individualised, all reaction steps should take place in a small space close to the point of care – the pharmaceutical factory in a compact, mobile “chest” would be a possible goal here.

As diverse as the applications are, as innovative are the solutions that reaction engineers develop and for which the plant engineers and equipment manufacturers provide the equipment.  In view of the numerous new developments, much can still be expected in the coming years.